1. Field of the Invention
The present invention relates generally to plastic pipe systems of the type used for transporting fluids, potable water, sewage, electrical power lines, telephone and communication lines and, more specifically to such pipe systems which are assembled together to form an inseparable end connection in operating conditions.
2. Description of the Prior Art
Plastic pipe systems formed from polyolefins and other plastic materials are widely used for a variety of applications at the present time. With the advent of plastic pipe materials such as polyethylene, polypropylene and polyvinyl chloride, a need has existed for connecting lengths of pipe together to form a string of pipes. Such pipe strings typically range from one half inch or so in diameter to over five feet and can extend hundreds of feet in length.
Forming pipe joints for plastic pipe strings has previously been problematical, especially where access to equipment and labor have been difficult. For example, polyethylene pipe is commonly used to replace or repair city sewage and drain lines with lengths of pipe being interconnected by butt fusion welding processes. The ends of the pipe lengths to be joined are melted and, in their softened state connected to one another. Commonly, the pipe sections are of 20 foot lengths and are interconnected by using expensive, difficult to operate butt fusion welding equipment which requires skilled personnel on the job site, making the process laborious and expensive.
Other types of end connections which have been used in the past have utilized external clamps, sleeves or other auxiliary paraphernalia. Such devices are less than advantageous since they require extraneous parts and since the protruding clamp portions of the devices always present the danger of becoming accidentally struck and damaged or causing the connection to be stuck within a surrounding conduit. For example, in slip-lining of underground pipe, such as sewer pipe, external clamping devices would prevent the pulling or pushing of the pipe through a larger conduit to be repaired.
Other problems in the prior art systems include the tendency of the connected pipe sections to pull apart while in service, with consequent damage to the pipeline and environment, as well as difficulty in locating the break for repair. Plastic pipe systems which do not include interlocking ends present problems when turning sharp corners as well as in situations where tensile forces are exerted on the pipe string, such as in an earthquake.
In addition to using external saddles and clamp assemblies, certain of the prior art systems require a minimal length to the bell and spigot portions of the connection in order to provide some play within the joint without losing a seal. This solution sometimes resulted in wasting extra lengths of pipe material and providing less than satisfactory insurance that the joint seal would not be broken.
It is an object of the present invention to provide an interlocked restraint for a plastic pipe joining system which features pairs of female and male integral end connections which can be snap fitted together to form a secure locked end connection with adjacent lengths of pipe forming a pipe joint. The snap joints of the invention are a very simple, economical and rapid way of joining two different components. It is only necessary that a protruding part of one component be deflected briefly during the joining operation in order to catch in a depression in the mating component.
Another object of the invention is to provide an interlocked restraint for a plastic pipe joining system that will reduce the bell length required, therefore minimizing the amount of pipe material required.
Another object of the invention is to provide an interlocked restraint for a plastic pipe joining system that will avoid overinsertion during assembly of the joint.
Another object of the invention is to provide such a secure end connection which is formed by the snap fit of the male connecting end axially into the female connecting end, taking into account the deformability characteristics of the plastic pipe being utilized.
Another object of the invention is that after the joining operation, the joint should return to a stress-free condition.
Another object of the invention is to provide such a secure interlocked end connection for a joint of plastic pipe which does not rely upon the use of external clamps, sleeves, saddles or other auxiliary paraphernalia.
Anther object of the invention is to provide such a secure end connection for a plastic pipe system which securely prevents the connected ends from pulling apart in service to thereby prevent damage to the pipeline and environment.